The present invention relates to a data storage apparatus for storing data in a form of a file, and in particular, to a technology for deleting a file efficiently while avoiding leaks of confidential information.
When storing data in a storage device such as a hard disc device, control information showing identification names (file names) of data, positions of storage and sizes are usually stored simultaneously in addition to substantive data. Since reading of the data is conducted by referring to the control information, deletion of the stored data is carried out by deleting the control information of the data, and the substantive data are not deleted.
However, in the method of deletion of this kind, if an special software is used, the data which ought to have been deleted can be read after being revived, because the substantive data still remain without being deleted. This is not preferable in view of the point of avoiding leaks of confidential information, when an occasion where data are stolen together with a hard disc device is assumed.
On the other hand, for deleting substantive data, a method to overwrite the total area to be delete with specific eliminating data such as “all-zeros”, “all-ones” or a random value is used in many cases, and a load of processing for deletion of the substantive data is large. For example, a digital copying machine includes a machine model that stores image data inputted from a scanner or an outer interface in a hard disc device temporarily, and then, reads them out to conduct operations for printout, and deletes the substantive data of image data after outputting for preventing leaks of secrets. When an amount of data is increased by requirements of colorizing, higher resolution and speeding up, the processing of deleting the substantive data starts to fail to deal with, resulting in a fear that productivity of operation such as copying operation is lowered.
Therefore, there is proposed an image processing apparatus wherein, when conducting storage of new data in the course of practicing data deletion processing, storage of new data and deletion of the substantive data of former data are carried out simultaneously by interrupting currently-running processing for deletion, and by storing new data in the area that follows the position of the interruption (for example, see Patent Document 1).
However, in the method to interrupt currently-running processing for deletion, and to store new data on a portion following the position of the interruption, the deleting processing and storing processing need to operate in cooperation with each other, resulting in complicated processing. Meanwhile, in the image processing apparatus disclosed in Patent Document 1, image data are stored in a continuous storage area. However, when storing data as a file by using a file system, actual data are sometimes stored in fragmented areas, and file control becomes complicated, if new data are stored from halfway of a file being deleted.
[Patent Document 1] Japanese Patent Publication Open to Public Inspection No. 2005-159550